The mammalian fetal membranes

Abstract

Some of my colleagues entering the field of reproductive physiology have expressed dismay at the bewildering variety of structures involved in the maintenance of pregnancy in different species. They have also expressed a certain exasperation with the terminology used in describing it. This essay was written to provide them with a very broad picture and to facilitate their accumulation of detail in selected areas. It has proved useful to beginners, to some who are not primarily biologists and to some biologists who have found this part of the subject indigestible because its literature is scattered and difficult of access. The latter complaint has meanwhile been alleviated by the publication of Comparative Placentology (Steven, 1975) which offers a guide to further reading. References have been confined to a few of the classic texts, with some more recent publications that will provide access to the bulk of the relevant literature. For those entering on serious study of mammalian embryology or comparative placentology, this essay can only serve as an introductory survey, a preface to the literature. It deals only with structure and will not (in the words of the Editor of the book just referred to) "encourage that most dangerous of anatomical pursuits, the prediction of function from structure". The study of function depends on experiment, but knowledge of the structures involved is a prerequisite of planned experiment, and in no other area of mammalian physiology is there such variety as is to be found in the means by which animals of different species contrive to retain, nurture and finally expel their young.